1. Field of the Invention
The present invention relates generally to vehicle steering wheels. More particularly, the present invention relates to an improved technique for passing electronic information between a steering wheel electronics assembly and a vehicle system that employs a programmable current source.
2. Discussion of the Related Art
In the automotive industry, steering wheels commonly provide drivers with a number of automotive controls such as cruise control, braking, flashing front lights, and flashing rear lights that are operated by electronic push buttons located on the steering wheel. These push buttons generate electronic information to be used by the vehicle when performing the various automotive functions. Existing techniques pass the electronic information from a steering wheel electronics assembly to an electronic control box, located under the dashboard or elsewhere in the vehicle. The steering wheel electronics assembly is generally located in the center of the steering wheel and can have the various electronic push buttons and lights mounted on it to operate the vehicle systems. The rotary motion of the steering wheel in relation to the steering wheel column typically requires the placement of one or more sliding contacts in the column in order to pass the electronic information from the steering wheel to the electronic control box. Typically, the steering wheel electronics assembly uses a time bit sequence of information and signal magnitude to convey to the electronic control box which particular button was pushed. In turn, the electronic control box decodes the electronic information and activates the appropriate automotive circuit within the vehicle. This circuit technique is fairly complex and difficult to maintain particularly due to the bit sequencing algorithms and circuitry required.
Another significant problem with this circuit technique for transmitting signals from steering wheel to a vehicle system concerns the contact resistance of the sliding contacts. The sliding elements of the sliding contacts are typically spring loaded and very prone to oxidation and other causes of surface degradation. If the electrical resistance between the sliding elements of a contact is too large, there will be an increased voltage drop across the sliding elements which decreases the overall system noise margin. The result is that the electronic control box cannot interpret the signal magnitude, and the system will either fail to operate or operate intermittently. This failure to operate properly is a source of great frustration to the driver, reduces system reliability, and causes numerous and costly repairs. Thus, there is a need to combat the problem created by high contact resistance of sliding contacts without increasing the cost of overall system operation.